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The supervolcano that lies beneath Yellowstone National Park
might have erupted less powerfully but more frequently than
previously thought, new research suggests.

In the ancient past, the
supervolcano at Yellowstone led to some of the largest-known
continental eruptions in Earth's history. Each of the world's
roughly one dozen
supervolcanoes is capable of spewing up to thousands of times
more magma and ash than any eruption ever recorded in human
history.

Scientists now find that the biggest Yellowstone eruption — the
fourth-largest known to science, which created the
2-million-year-old Huckleberry Ridge deposit — was actually at
least two different eruptions that occurred about 6,000 years
apart.

Sharper focus

To see when the eruptions took place, the researchers analyzed
rocks from Yellowstone to look at isotopes of particular elements
(isotopes have different numbers of neutrons in their nuclei).
The rate at which the isotope potassium-40 radioactively decays
to become the isotope argon-40 is known, and by analyzing the
ratio of argon and potassium isotopes within these rocks,
researchers could determine when they were laid down by
eruptions. [ Infographic:
The Geology of Yellowstone ]

Researcher Darren Mark at the Scottish Universities Environmental
Research Center recently helped improve this dating technique by
1.2 percent — a small-sounding difference that can become huge
across geologic time.

"It's like getting a sharper lens on a camera — it allows us to
see the world more clearly," Mark said.

The new ages for each Huckleberry Ridge eruption reduce the
volume of the first event to about 530 cubic miles (2,200 cubic
kilometers), roughly 12 percent less than previously thought. A
second eruption of about 70 cubic miles (290 cubic km) took place
more than 6,000 years later. In comparison, the 1980 eruption of
Mount St. Helens produced just about a quarter of a cubic mile (1
cubic km) of ash.

The first Huckleberry Ridge eruption still deserves to be called
"super." By itself, it is the fourth-largest known to have
occurred on Earth, darkening the skies with ash from southern
California to the Mississippi River, said researcher Ben Ellis, a
volcanologist at Washington State University.

"The big eruptions from Yellowstone are certainly still big,"
Ellis told OurAmazingPlanet.

More frequent eruptions

By knowing how this supervolcano behaved in the past, scientists
can now better predict what it might do in the future.

"This research suggests explosive volcanism from Yellowstone is
more frequent than previously thought," Ellis said.

These findings, detailed in the June issue of the journal
Quaternary Geochronology, suggest that other supereruptions might
actually be multiple, closely spaced eruptions as well.